The research work presented in this thesis is concerned with an investigation of fuel management of diesel engines for the purposes of developing control schemes to improve fuel consumption, exhaust emissions and engine controllability.

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The Thesis can be broadly classified into 2 sections. Initially it attempts to solve an existing long-term problem in the spark plug manufacturing industry, namely reliability and criteria for spark plug production testing. The second section of the Thesis develops the preliminary work and explores the fundamental theory of ignition sparks in preparation for the main study of ignition system and ignition spark mathematical modelling. Section 1 of the Thesis begins by introducing spark plug faults and existing production faults detection equipment and methods. An evaluation of potential new fault detection and classification systems follows, in two phases: detection and analysis. A suitable electrical test and neural network based production test system is then derived from the preceding work. This first section of the Thesis culminates in a factory evaluation of the prototype system at the sponsoring company. Section 2 of the Thesis uses experience gained from Section 1 to effect an investigation into the fundamentals of ignition spark development, leading to the mathematical modelling of Kettering-type ignition systems and associated spark profiles. Finally, the practical benefits of the modelling are discussed with respect to potential real automotive applications. There are two main novel aspects of the work. (1) The use of a neural network to analyse and classify ignition spark waveforms is believed to be a novel idea which can be further extended in many areas beyond the spark plug testing application discussed here. (2) Ignition system and spark modelling is a relatively unexplored research area. This work has resulted in an increase in the level of complexity of model and therefore a potential increase in precision.

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There are two important omissions in the literature on bore polishing, firstly there is no evidence of the successful development of a reliable tribo test device to simulate bore polishing and secondly, the mechanism of bore polishing has not been fully defined. The aims of this study were: 1. To establish the principal characteristics of bore polishing In engines. 2. To produce bore polishing in the laboratory. 3. Differentiate between two reference oils in a laboratory tribo test. 4. To understand the mechanism of bore polishing. The principal characteristics of bore polishing have been identified by the examination of Tornado cylinder bores from an engine test. The graphite structure is visible on the surface which has a surface finish of less then 0.125 micro-m in C.L.A. value. The components used in these tests were a grey cast iron piston ring running on a grey cast iron cylinder bore typically used in commercial engines. A reciprocating tribo test was used to distinguish between the two reference oils. The result showed higher friction, wear and a smoother surface with the oil causing bore polishing compared to the other oil which did not produce bore polishing. Adding carbon, taken from the wall of a piston used in an engine test, to the lubricant in the laboratory tribo test produced a phenomenon resembling bore polishing. Comparisons have been made between the tribo test results and service engines and a good correlation has been obtained. Several analytical techniques have been used and the knowledge of bore polishing has been advanced. In particular, it is suggested that a combination of two processes, one mechanical and the other chemical, are associated with bore polishing. Four wear mechanisms were identified during this investigation; abrasion, delamination, corrosion and adhesion.

This work concerns the prediction of potentially damaging thermoacoustic oscillations in gas turbine combustion systems by computational means. A framework is laid out to predict numerically the frequency and stability of thermoacoustic oscillations, with focus on the high frequency screech instability of afterburners. A hybrid numerical method is used that includes separate calculations of the mean flow and of the perturbed field due to the acoustic oscillations. This modularity supports the choice of models that are the most appropriate for combustion and for acoustic wave propagation, which are the processes that make up the feedback mechanism that can lead to the establishment of an instability. This gives flexibility, improved accuracy and more insight into the physics of the thermoacoustic system at a potentially reduced computational cost. The mechanism leading to screech involves the formation of vortices induced by acoustic transverse modes at the afterburner flameholder. These vortices trap fresh reactants that burn after a certain time delay, therefore feeding energy into the oscillation. Within a linear approximation, the effect of small amplitude acoustic fluctuations on the flame is studied by perturbing harmonically the transverse velocity at the flameholder lip over a range of frequencies using forced combustion CFD calculations. The response in heat release rate, which is a thermoacoustic source of sound, is represented by a flame transfer function (FTF). It is argued that for the investigation of screech oscillations, this FTF must be multi-dimensional because of the transverse nature of the acoustic oscillation. For fully premixed flames, the main contributor to heat release rate fluctuations is the variation in flame surface area. This information is used to develop a novel flame model that represents the multi-dimensional, frequency dependent response of the flame to velocity perturbations. Compared to FTFs, which require computationally expensive forced calculations, this model has the advantage of providing the frequency dependent flame response as part of the acoustic calculation. After verification and validation of each of the tools used for the acoustic and combustion simulations, this flame model is used in the analysis of a simplified afterburner, where a high frequency, radial and longitudinal resonant mode was computed. Convective modes, which are important in the prediction of the frequency of thermoacoustic oscillations are predicted as a result of the interaction between the acoustic wave and the flame.

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